There are things that are really only a medium of exchange *or* a store of value, but they don’t make very good money so they aren’t used (alone at least). Bulk commodities are stores of value because their relative worth to the economy tends to stay pretty stable, but you don’t want to use trucks of gravel or silos of grain as money. Similarly, things like limited time coupons are a sort of medium of exchange, but they don’t really store value because they turn into a pretty worthless piece of paper after a short time so they can’t be your only form of money
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